1. Field of the Invention
The present invention relates to a protein having a β1,3-galactosyltransferase activity, a DNA encoding the protein, a recombinant DNA containing the DNA, a transformant containing the recombinant DNA, a method for producing a protein having a β1,3-galactosyltransferase activity using the transformant, and a method for producing a galactose-containing carbohydrate using the transformant.
2. Background Art
Regarding β1,3-galactosyltransferase genes, the genes derived from higher animal (J. Biol. Chem., 273: 58 (1998), J. Biol. Chem., 273: 12770 (1998), J. Biol. Chem., 274: 12499 (1999)) have been obtained. However, since it is generally difficult to express the genes derived from higher-animal as active proteins in microorganisms, a β1,3-galactosyltransferase gene derived from higher-animal has not been expressed as an active protein in a microorganism such as Escherichia coli or the like.
On the other hand, in microorganisms, there is a report stating that a β1,3-galadtosyltransferase gene was obtained from Campylobacter jejuni and the gene was expressed in Escherichia Coli. However, although this enzyme has an activity of transferring galactose to N-acetylgalactosamine, there is no report about the activity of transferring galactose to N-acetylglucosamine (J. Biol. Chem., 275: 3896 (2000)).
Human milk abundantly contains galactose-containing carbohydrates, lacto-N-tetraose being one of the main components (Acta Paediatr., 82: 903 (1993), J. Pediatr. Gastroenterol. Nutr., 30: 181 (2000)). Since it is known that lacto-N-tetraose and lacto-N-neotetraose, which are the galactose-containing carbohydrates, are recognized by Pseudomonas aeruginosa (Infect. Immun., 59: 700 (1991)), the galactose-containing carbohydrates are considered to be strong candidates for safe antiinfection drugs which can prevent human body from infection with Pseudomonas aeruginosa. 
Regarding production of a galactose-containing carbohydrate such as lacto-N-tetraose or the like, both the methods of extraction from human milk and chemical synthesis are known but such methods have problems in terms of cost and productivity, so that its industrial production method has not yet been established.